U.S. Pat. Nos. 3,789,832 and 4,354,499 to Damadian disclose a nuclear magnetic resonance (hereinafter NMR) instrument and a method for forming images of the internal organs of a patient that aid physicians in diagnosing illnesses. Advantageously, the procedure is performed without subjecting the patient to X-rays that may damage tissue.
A patient is positioned within the NMR instrument that includes a large circular magnet. The magnet produces magnetic fields about 6000 times as strong as the magnetic field of the earth. These strong magnetic fields cause certain "nuclear magnets" in the patient's body to line up in the direction of the field. A radio wave of a chosen frequency is then beamed through the patient. Some of the nuclei that lined up in the magnetic field absorb the radio wave energy and flip so that their nuclear magnets change direction. When the radio wave transmission is terminated, the realigned nuclei return to their original orientation in the magnetic field emitting characteristic and detectable radio signals as they flip.
Neither the transmission of magnetic fields or radio waves through the body damages the tissue. Further, the resulting radio signals from the nuclei indicate how many atoms of a certain kind are at a particular point in the sample since the magnetic strength of each differs from the strength of others.
A computer combines the signals from the nuclei so as to construct an accurate image of the interior of the body of the patient. It is this image that is displayed on a video screen or printed so that the physicians can study it. The NMR instrument enables a physician to look at details of the body structure. Specifically, the resulting image allows the detection of possible disease through tissue that looks unusually light or dark.
Should the physician uncover a scan image of particular concern, he undoubtedly will wish to obtain further information by scanning at a slightly different location or angle. This may be done by utilizing the image slice offset and/or image slice angulation features of the instrument. The image slice offset relates to the distance moved along a scanning axis from one scan position to another. The image slice angulation relates to the angle at which the scan is aligned with respect to the scanning axis and the perpendicular. It, however, should be appreciated that it is imperative that the image slice offset and angulation are being properly indicated by the instrument so that the physician may accurately choose a field or plane of scan, and in turn receive an accurate picture of the tissue in question.
The parameters of image slice offset and angulation, are particularly difficult to verify as no actual hardware within the NMR instrument moves as the field of scan is moved. Rather, the electrical current to the magnet surrounding the patient is altered so as to change the magnetic gradient and move the field of scan. Thus, the scan positioning is software controlled and there can be no visual verification of the angulation and offset through the examination of the instrument itself.
Consequently, a need is identified for an apparatus and method allowing the verification of NMR instrument image slice offset and angulation. In particular, the on-site verification of image slice offset and angulation advantageously enables the physician to confidently and accurately position the field of scan so as to obtain the desired scan image allowing improved diagnosis of patient tissue, and thus the illness. Further, this need exists with all computed tomographic imaging instruments and methods such as X-ray computed tomography and positron emission tomography.